1 . Field of the Invention
The present invention relates to field of silicon microphone, more specifically, to an MEMS silicon microphone and a manufacture method thereof.
2 . Description of the Related Art
Microphone converts human voice into a corresponding electrical signal, and is widely used in intelligent terminals like mobile phones, computers, telephones, cameras and camcorders.
Advancement in development of MEMS (Microelectromechanical Systems) technology and process in the last thirty years and so, particularly development of silicon-based MEMS technology, has resulted in miniaturizing a number of sensors with low cost. Started in applications in high-end smart phones, MEMS silicon microphones have found their use broadening over the years in what has become a fast-growing and huge market.
MEMS microphone mainly uses capacitive principle, comprising a diaphragm and a backplate with a few microns of air gap between the two, which forms a capacitor structure. Once the highly sensitive diaphragm senses the external acoustic pressure, the gap between diaphragm and backplate will change, thereby resulting in a capacitance change. The MEMS microphone is connected with a CMOS amplifier and an integrated charging pump for biasing the microphone. The capacitance change will be then converted to a voltage change as an electrical output.
The diaphragm must be thinned down to a specific thickness so that it is very sensitive to the weak human voice signal. Based on the prior art, the fabrication of diaphragm suffers hardly controllable residual stress, significantly affecting the diaphragm sensitivity.
The traditional diaphragm is mainly made of polysilicon or a stack of metal and silicon nitride. Several methods are used to increase the diaphragm sensitivity: first, in case of LPCVD polysilicon film used as diaphragm, an additional annealing process has to be used to adjust the residual stress to a low level; second, for the LPCVD silicon nitride film used as diaphragm, the ratio of reactive gases and deposition temperature are adjusted to reduce residual stress. Unfortunately, all these two methods are not effective and complicated with limited reproducibility; third, the change of diaphragm structure, such as corrugated or floating diaphragm, or the introduction of some small grooves on the diaphragm can also reduce the residual stress and improve sensitivity. However, this kind of methods will result in process complication, cost increase and yield reduction.
Therefore, how to solve the above technical defects becomes a research focus for technical personnel in MEMS microphone field.